The present invention relates to a process for preparation of a seed layer for selective metal deposition on a substrate. More particularly, it relates to a process utilizing a laser for preparation of a seed layer for selective metal deposition.
Lasers and other directed energy sources such as ion and electron beams have been used to deposit and etch materials on surfaces. They have also been used to cause thin layers of materials to mix, alloy or react for various purposes. For example, U.S. Pat. No. 4,574,095 discloses the use of an excimer laser to deposit palladium onto a surface from a liquid precursor for the purpose of speeding a subsequent electroless plating process. Similarly, U.S. Pat. No. 4,701,347 teaches a method of laser depositing material from a metallorganic vapor which catalyses the subsequent deposition of metal on the laser-treated surface.
U.S. Pat. No. 4,555,301 discloses the use of a laser to cause the melting of a layer of nickel (Ni) on crystalline silicon (Si) to form substantially monocrystalline nickel silicide (NiSi2). Still another example, as disclosed in U.S. Pat. No. 4,495,255, is the use of a laser to cause alloying of gold (Au) with nickel (Ni) to form a good electrical connector. In addition, a pulsed laser is described in U.S. Pat. No. 4,877,644 which can be used to ablate a polymer masking layer off an underlying metal seed layer to permit deposition on that exposed metal.
The present invention relates to creation of plated metal interconnects from the surface of an integrated circuit (IC) chip, down the side of the chip, to contacts on the underlying silicon circuit board. Conductors are to be formed on the vertical sides of the chip, as well as on horizontal surfaces. Liquid precursors of a seed layer such as are used in U.S. Pat. No. 4,574,095 are unsatisfactory since they do not adequately cover the vertical surfaces on top edges. Liquid polymer precursors used in U.S. Pat. No. 4,877,644 are unsatisfactory of the same reason. Direct laser deposition of the entire conductor from the vapor phase has the disadvantage that deposition is too slow to be practical.
U.S. Pat. Nos. 4,555,301 and 4,495,255 describe alloying two or more materials, however, the laser step was not followed by a further deposition step.
U.S. Pat. No. 4,348,263 to Draper et al, discloses laser irradiation of a surface followed by electroplating, but the laser step does not form the alloy nor does it activate an otherwise inert surface for electroplating. The initial surface is active and the laser is only used to improve the surface morphology.
It would be desirable in the art to provide a process for activating a surface layer in a predetermined pattern suchh that metal could be selectively deposited thereon, and electronic circuits or interconnects formed. This invention is concerned with such a process.